Mechanical properties of molybdenum disulfide nanoribbons with armchair edges

Ishikawa Japan--The properties of nanoribbon edges are important for their applications in electronic devices, sensors, and catalysts. Recently, a group of scientists from Japan and China studied the mechanical response of single-layer molybdenum disulfide nanoribbons with armchair edges using in situ transmission electron microscopy. They showed that the nanoribbon Young’s modulus varied inversely with its width below the width of 3 nm, indicating a higher bond stiffness for the armchair edges.

Sensors have become ubiquitous in the modern world, with applications ranging from detecting explosives, measuring physiological spikes of glucose or cortisol non-invasively to estimating greenhouse gas levels in the atmosphere. The primary technology required for sensors is a mechanical resonator. Traditionally, quartz crystals have been used for this purpose owing to their high rigidity and easy availability. However, this technology has recently given way to advanced nanomaterials. One such promising material is the single-walled molybdenum disulfide (MoS₂) nanoribbon.

Characterizing the physical and chemical properties of nanoribbon edges is crucial for their applications in electronic devices, sensors, and catalysts. However, the mechanical response of MoS₂ nanoribbons—expected to be dependent on their edge structure—has remained unexplored, hindering their practical implementation in thin resonators.

Against this background, a group of scientists from Japan and China, led by Professor Yoshifumi Oshima from Japan Advanced Institute of Science and Technology (JAIST), has recently investigated the mechanical properties—namely the Young’s modulus—of single-layer MoS₂ nanoribbons with armchair edges as a function of their width using a micromechanical measurement method.

Their work, published in the journal Advanced Science, was co-authored by Associate Professor Kenta Hongo and Professor Ryo Maezono from JAIST and Lecturer Chunmeng Liu and Lecturer Jiaqi Zhang from Zhengzhou University, China.

Prof. Oshima describes their work in detail: “We have developed the world’s first micromechanical measurement method to clarify the relationship between the atomic arrangement of atomic-scale materials and their mechanical strength by incorporating a quartz-based length extension resonator (LER) in an in situ transmission electron microscopy (TEM) holder.” Since the resonance frequency of a quartz resonator changes when it senses contact with a material, the equivalent spring constant of the material can be estimated with high precision by the change in this resonance frequency. Moreover, it is possible to capture high-resolution TEM images as the LER vibration amplitude necessary for the measurement is as small as 27 pm. Consequently, the novel method developed by the researchers managed to overcome the shortcomings of conventional techniques, achieving high-precision measurements.

The researchers first synthesized a single-layer MoS₂ nanoribbon by peeling off the outermost layer of the folded edge of an MoS₂ multilayer using a tungsten tip. As a result, the single-layer nanoribbon was supported between the multilayer and the tip. The TEM image of this MoS₂ nanoribbon revealed that its edge had an armchair structure. “The width and length of the nanoribbon were also measured from the image, and the corresponding equivalent spring constant was determined from the frequency shift of the LER to obtain the Young's modulus of this nanoribbon,” elaborates Lecturer Chunmeng Liu.

The researchers found that the Young’ modulus of the single-layer MoS₂ nanoribbons with armchair edges was dependent on their width. While it remained constant around 166 GPa for wider ribbons, it showed an inverse relation to the width for ribbons below 3 nm in width, increasing from 179 GPa to 215 GPa as the nanoribbon width decreased from 2.4 nm to 1.1 nm. The researchers attributed this to a higher bond stiffness for the edges compared to that of the interior.

Moreover, density functional theory calculations performed by the researchers for explaining their observation revealed that the Mo atoms buckled at the armchair edge, which resulted in electron transfer to the S atoms on both sides. This, in turn, increased the Coulombic attraction between the two atoms, enhancing the edge strength.

This study thus sheds important light on the mechanical properties of MoS₂ nanoribbons, which could facilitate the design of nanoscale, ultra-thin mechanical resonators. “Nanosensors based on such resonators can be integrated into smartphones and watches, which will enable people to monitor their environment as well as communicate the sense of taste and smell in the form of numerical values,” concludes an optimistic  Lecturer Jiaqi Zhang.

 

 

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Reference

Title of original paper:	Stiffer bonding of armchair edge in single-layer molybdenum disulfide nanoribbons
Authors:	Chunmeng Liu, Kenta Hongo, Ryo Maezono, Jiaqi Zhang*, Yoshifumi Oshima*
Journal:	Advanced Science
DOI:	10.1002/advs.202303477

 

                                         

 

About Japan Advanced Institute of Science and Technology, Japan

Founded in 1990 in Ishikawa prefecture, the Japan Advanced Institute of Science and Technology (JAIST) was the first independent national graduate school in Japan. Now, after 30 years of steady progress, JAIST has become one of Japan’s top-ranking universities. JAIST counts with multiple satellite campuses and strives to foster capable leaders with a state-of-the-art education system where diversity is key; about 40% of its alumni are international students. The university has a unique style of graduate education based on a carefully designed coursework-oriented curriculum to ensure that its students have a solid foundation on which to carry out cutting-edge research. JAIST also works closely both with local and overseas communities by promoting industry–academia collaborative research.

 

 

About Professor Yoshifumi Oshima from Japan Advanced Institute of Science and Technology, Japan

Yoshifumi Oshima is a Professor at the Nanomaterials and Devices Research Area, Japan Advanced Institute of Science and Technology (JAIST). He obtained his B.S. degree from Tokyo University of Science in 1989 and M.S. and Ph.D. degrees from Tokyo Institute of Technology in 1991 and 2001, respectively. He worked as a researcher at JST (2007) and a Research Associate Professor at Osaka University (2010). His research interests include nanomaterial properties that are strongly correlated to their atomic structure and shape. His group studies them by developing transmission electron microscope holders combined with atomic force microscopic technique or the related techniques. He has published around 200 research papers, which have been cited over 2,500 times.

 

Funding information

This study was supported by JSPS KAKENHI (Grant Nos. 18H01825, 18H03879, and 23H002255), the China Scholarship Council under Grant No. 201808050001 and the support of the Sasakawa Scientific Research Grant from The Japan Science Society (No. 2021–2011), the Sasakawa Scientific Research Grant from The Japan Science Society (No. 2020–2006) and the Exchange Research Grant Project from Marubun Research Promotion Foundation.

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